Relationships between anthropometric measures, body proportions, weight and penile dimensions in young adult males have not been previously analyzed. Furthermore, although male fertility has declined in last decades, no data on testicular volume (the best surrogate measure for spermatogenic potential) are available for the general population of young men in Italy. To analyze anthropometric measures and proportions, testicular volumes, and penile dimensions in a large cohort from the general population of young Italian men aged 18-19 yr. MATERIALS/SUBJECTS: We analyzed 2019 students aged 18-19 years for height, weight, body mass index (BMI), waist circumference, arm span, pubis-to-floor and crown-to-pubis length, and penile dimensions. Testicular volumes were measured by ultrasound in 776 subjects. Thirty-six percent of the subjects had a pathological arm span-height difference (>3 cm) and 44.7% had a pathological pubis-to-floor/ crown-to-pubis ratio (≤ 0.92). The mean penis length was 8.9 ± 1.4 cm and the penis circumference was 9.5 ± 1.0 cm. BMI was positively associated with arm span-height difference and negatively with penis length; 23.2% of the subjects had low mean testicular volume (<12 ml). The findings highlight a strong influence of BMI on skeletal proportions and penis length, identify a large proportion of subjects with testicular hypotrophy at risk for future fertility, and suggest to consider worldwide studies to redefine normal values for arm span-height difference and upper/ lower body segment ratio.